Thin Kerf Blades

You were on the right track of using a thin blade on a low HP saw and also it wastes less wood in the cut. But, thin blades are prone to flexing on thick or hard wood which is a problem in making precise cuts.

Lots of small details like this to learn. In 40+ years I’m still learning. I guess that is the attraction of woodworking.

-- Les B, Oregon

Hi Les,
Yes – I was hoping the thin kerf would have worked out. But, I was only cross cutting a 1×3 and the difference in quality of cut was huge.

1. Do you guys have a favorite normal (thick) kerf 7 1/4” cross cut blade?

And

2. Same question for ripping? Favorite 7 1/4” normal kerf ripping blade?

Blades that won’t flex too much (if at all).

Thanks, Steve

For thin kerf blades, saw blade stabilizers will help.
My favorite blades are Tenryu. Their selection is vast. My Skill 77 loves the Tenryu PT-18540B 7 1/4 blade.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

I didn’t think 7 1/4” blades came in different kerfs.

One thing about miter gauges, if you don’t have a stop block, clamping the piece to the fence can be the difference between a clean cut.

Have you checked to see the miter slot it parallel to the blade?

-- Everything is a prototype thats why its one of a kind!!

Yea. With stop block and without – same result.
The saw is pretty well aligned-at least as good as I can with respect to the adjustment capabilities of the saw. Blade is parallel to miter tracks. Fence is parallel to miter tracks (and blade). And miter gauge is square to miter tracks.
It’s the blade.
What I’m guessing is happening is—
The blade starts cutting square. But as it progresses, it flexes in the direction of the off cut. I think this is happening because the off cut side is lessening pressure against the blade as it’s being cut away. However, the good piece side of the wood stays in position which keeps slight pressure on the teeth. This differential is causing the cut to slightly angle. This doesn’t happen with the thicker blade. The cut is nice and true.
Now. I may be totally off base with this analysis. But, it’s what I think at this point.

And – I’m new to all this. So, I don’t know if manufacturers are making only thin kerf 7 1/4” blades these days. I happened to have an old Craftsman 7 1/4” which is a thick kerf blade.

A framing blade is called that because it’s designed for cutting framing (construction) lumber as quickly as possible where clean cutting is not needed. It might work OK for you for ripping, but crosscutting or cutting miters is definitely not its best use. For a clean miter cut, a blade with more teeth would be better.

In the 10 inch blade category, rip blades are frequently about 24 teeth, combination blades about 40 teeth, and blades designed to crosscut are frequently 60-80 teeth; the shapes of these teeth differ as well. A 9” blade might have fewer teeth, but often not too far from these numbers. Try to find an inexpensive blade designed for the work you want to do, and test that before deciding the kerf is the culprit. You want something that says it cleanly crosscuts.

Are you making a miter cut at 45 degrees, or are you crosscutting at 90 degrees? Sometimes terminology can get in the way.

Definitely focus on the blade, but keep in mind that some blades are more forgiving of small saw misalignment than others. At some point you may benefit from a return to that topic.

-- Alan in Wisconsin

I didn’t get to testing 45 deg cuts yet. The issue I’m having is at 90 deg cross cuts.
I went with that specific framing blade because that youtube video on taming your table saw seems to recommend that one. He loves that blade.
My preconceived notion about a framing blade is that it would probably create rougher cuts with more tear out than a specific cross cut blade. But, I didn’t expect it to not cut square as compared to another 7 1/4” 24 tooth thicker blade.
Yea. I was thinking of trying out a Freud higher tooth count cross cut blade. I’m pretty sure it’ll cut smoother. But now, I’m now worried that it too won’t cut square.
So, I was trying to avoid buying a bunch of blades that I might end up never using. So, I was trying to get a little bit of a feel as to what blade to try next from you guys. I was hoping some of you guys might have experienced something similar to what I am.
And of course, there could always be some misalignment that got by me. But, I don’t think I can align this saw any better. I was getting repeatable alignment numbers with a dial gauge to within 2 to 3 thousandths on all measurements – which I think are pretty good numbers for this saw. I’m not perfect. So, I could have screwed up the alignment process somewhere. But, I don’t think I did.

I had that same problem, even after building a 45 degree sled for box miters. I did exactly the same thing you did with a 7 1/4 blade. It has solved my problems.

If you get sufficient depth of cut with a 7 1/4” blade, use that size for now. They are much cheaper than less standard sizes: this thin kerf 40 tooth blade should cut cleanly and is under $15.

https://www.amazon.com/Freud-D0740A-Finishing-Knockout-PermaShield/dp/B00008WQ2G?th=13 .

It sounds like you did a careful job of alignment. You may have gotten a bad blade. If you cut very slowly you can probably minimize the problem, but I suspect it’s not simply due to the thin kerf.

-- Alan in Wisconsin

...
It s the blade.
What I m guessing is happening is—
The blade starts cutting square. But as it progresses, it flexes in the direction of the off cut. I think this is happening because the off cut side is lessening pressure against the blade as it s being cut away. However, the good piece side of the wood stays in position which keeps slight pressure on the teeth. This differential is causing the cut to slightly angle. This doesn t happen with the thicker blade. The cut is nice and true.
Now. I may be totally off base with this analysis. But, it s what I think at this point.
...
- skess

A couple of things:

You say you’re a newbie, so there may be issue with your technique. Try making the cut with the wood clamped to the miter gauge so that you can eliminate any side-to-side pressure and check your cut. Use one hand on the miter gauge handle to push it through rather slowly to give the teeth time to remove the waste. Do not touch the wood or the miter gauge with the other hand. (A thicker blade might be able to withstand any pressure to the side of the blade better than a thin kerf blade)

If that didn’t correct the issue then it is probably not a technique issue, so you need to test the hypothesis of the blade flexing during the cut.

Mark the the top of your board with an arrow pointing toward the blade and make a cut. Verify that it is NOT 90 degrees.

Put the board back on the miter gauge with the arrow pointing toward the blade again. Line the very front corner of the wood up with the blade such that the front corner barely kisses the blade. It should be almost cutting nothing.

Push the wood slowly through the blade. It should not cut very much from the front of the cut, but start cutting more and more as you push it past the blade.

If it cuts more at the back of the original cut than the front, then there is an issue with the blade flexing.

If it doesn’t cut anything or cuts parallel to the original cut, then you have a setup issue.

-- Tony, SW Chicago Suburbs

Thanks guys –
I had thought that my hand might have been exerting inadvertent pressure on the wood.
So yws, I had tried clamping the piece to the miter and only pushed the miter – without touching the wood. I also tried using the miter with a long piece of wood as backing so that the piece had more support. Plus, I extended the edge past the blade so that there was support for both the good piece and the off cut. That didn’t make a difference. Still got the not square result.

Tony – I’ll try the hypothesis test next when I get a chance. Thanks for the tip.

Alan – thanks for the link. I’d like to try that blade out.

I had that same problem, even after building a 45 degree sled for box miters. I did exactly the same thing you did with a 7 1/4 blade. It has solved my problems.

- BurlyBob

Hey Bob,
When you say you did the same thing I did – you mean you switched to a full (thicker) kerf 7 1/4” blade?

Thanks,
Steve

Tony – I ran the test that you described and definitely the blade flexing.

I then put the thicker blade back on and made a cut and it was square again.

Then, I tried the same test with a 3/4” plywood scrap – about 7” if a cross cut. Same result.
Also, the Freud blade really burnt the edge. The thicker blade didn’t burn at all.
My blade height has about 1/4” to 1/2” of the blade above the piece of wood. So, it shouldn’t be prone to burning since the teeth are only engaged at the beginning and the end of the cut.

When I get the 40 tooth freud finishing blade – I’ll see how that does. But, my preconceived notion is that the cut will be smoother but that it will flex also. Hopefully, I’ll be proven wrong about the flexing.

I’d like to try ripping with this freud blade to see how it performs with that. But, I’m afraid to rip until I get some sort of splitter in place. I’m still thinking about what to do about that – diy or look for some aftermarket solution.

That’s today’s update.

One further comment re: using the miter gauge. When pushing the wood through the blade, make sure you apply lateral pressure on the miter gauge toward the blade. A few thousands “slop: between the miter gauge bar and the table slot can throw off the cut.